Meet Mark Wallace, NASA's Interplanetary Travel Agent

"Thank you for having me!" he says at the end. "Any questions?" In a tiny, hole-in-the-wall art gallery in central L.A., a rocket scientist is wrapping up a talk titled "Getting There: Science Fiction ... and Fact." The gallery founder, wanting to add a bit of oomph to a space-related exhibit, had rung up NASA to request a speaker. They sent him Mark Wallace, Jet Propulsion Laboratory mission analyst and self-described "interplanetary travel agent." One engineering nerd, coming right up: glasses, rumpled khakis, ID badge, bemused expression, Wikipedia-like brain.

If the solar system is the spinning Mad Hatter's tea party ride, and Wallace is sitting in one cup with a ball in his hand, his target located in a cup across the room, his job is to figure out how to throw the ball not where that cup is but where it is going to be. Complicated enough -- but now imagine that his ball is a spaceship, and making the target is a matter of triumph or disaster. "It's a job," he says, "that severely messes with your concept of 'now.' "

Now, it is approximately 8 p.m. Now, on Wallace's final slide, Star Trek's USS Enterprise is cruising out of orbit. Thirty folding chairs, 18 occupied -- the room in Home Room gallery is small, but the questions are big.

A man raises his hand. What happens if there's an outer-space collision?

Junk floats in a cloud around the Earth. Recently, it's come from China. In January, the International Space Station dodged pieces of the defunct Fengyun 1-C weather satellite. American and Dutch astronauts took refuge in a Russian Soyuz capsule and waited on tenterhooks to see if the Chinese debris would pierce their hull and send them to an early, cross-cultural grave. (It didn't.)

Space is nifty, but it's also "a really nasty place," Wallace opines. Astronauts get cataracts from the radiation. Microgravity causes their bones to undergo accelerated osteoporosis. Sadly, they never do get that bone density back.

Another hand. Another line of inquiry. What does he think of Mars colonization?

"Well, it's not like colonizing the New World," Wallace says. "On Mars, you step outside and you die."

Next?

As an insider, a guy asks, how does Wallace feel about NASA not having a clear mission? Wallace shrugs. He speaks for himself, not for NASA. "A lot of it is being driven by the economy and the deficit hawks." NASA has a directive to send an astronaut to an asteroid by 2025. "It's three presidents away," he says -- a blip in galactic time but an eternity in bureaucratic time. It's not clear if the political will can survive until then.

The human space flight program has been rudderless for the past 25 years, he continues. We spend a half-penny per tax dollar on NASA, while the Department of Defense gets 30 cents. You do the math.

By comparison, the private sector is bustling. It's planning to mine asteroids. It's selling $200,000 seats on commercial spaceships to millionaire wannabe astro-tourists. "According to international law, you can totally mine an asteroid," Wallace says. "But if you bring anything back, you have to give all of it away to developing countries. The asteroid is not yours, in other words. It belongs to mankind."

"What sorts of minerals would there be of serious value to mine on an asteroid?" a girl asks.

As it turns out, platinum-group metals are more expensive than gold, and "the asteroids are kind of covered in them," Wallace says. They're also covered in the rare earth metals that are so difficult to mine here in an ecologically friendly way.

"But then again," Wallace notes, "if you bring back several metric tons of platinum, what's that going to do to the price of platinum?"

People chuckle.

Conversation turns to Saturn. When a woman in the front row requests the size of the particles that make up its rings, Wallace curls his thumb and forefinger into a teeny circle. Some are dust grains. Some are huge as houses. Many are icy crystals of water -- snow, basically. Deep space snow. No one quite knows why Saturn's rings are the way they are.

"Now that is a very insightful question." Wallace's eyes brighten. He takes a loud breath. Venus, he says. To begin with, why does the same face of Venus point toward us every single time it gets between us and the sun? Is it a coincidence? "From a purely orbital-mechanics standpoint, it's absolutely mystifying."

For that matter, as far as neighbors go, Venus is almost our size. It's a similar distance from the sun. "It really should look a lot like us," Wallace says. "But it's a hell world." Its surface is hot enough to melt lead. Standing on Venus would be like standing at the bottom of the Arctic Ocean. Nuclear submarines can't even go that deep. They crush at 730 meters. How did Venus get to be that inhospitable, when everything about its orbit says it should be like us? "What happened? What went wrong?"

And Mars. There is "spectacular" evidence that Mars was once warm and wet. "It's not now," Wallace says. "Why? Where did that atmosphere go? What happened to Mars to eliminate that potential life-sustaining atmosphere? Is it something that could happen to us?"

The list of known unknowns is growing longer now, and the audience is growing quieter. What's under the ice crust covering the oceans of Europa, the Jupiter moon? Why is oddball Uranus tilted on its side? What causes the dark "spokes" that dance like shadows across Saturn's bands? These are questions about how the universe is put together.

"And, of course, the big ones," he says. "Are we alone?"

Now, on Earth, everywhere there's liquid water and a source of energy -- be it chemical or photonic -- we find life. "It doesn't matter the pH, the temperature, the pressure ... water plus energy equals life. Mars? Had water. Had energy. Is there life there?"

Should we discover a so-called "second genesis" elsewhere, it will be akin to discovering that the sun does not orbit the Earth. That it is not the center of the cosmos but rather an obscure star on the edge of the Milky Way, "a perfectly average galaxy," Wallace notes, "a big galaxy by intergalactic standards." He loves that he can say "by intergalactic standards" without hyperbole.

Knowledge of this sort would revolutionize our understanding of our place in the universe. "We are on the cusp of being able to learn the answer to those questions," he concludes.

And by "cusp," he means one or two very expensive, multidecade missions away. "I know that's a long answer to a pretty short question."